private function populate()
 {
     $article = new RelatedArticle();
     $article->setTitle('a1-t-v1');
     $article->setContent('a1-c-v1');
     $comment = new Comment();
     $comment->setArticle($article);
     $comment->setMessage('m-v1');
     $comment->setSubject('s-v1');
     $this->em->persist($article);
     $this->em->persist($comment);
     $this->em->flush();
     $comment->setMessage('m-v2');
     $this->em->persist($comment);
     $this->em->flush();
     $comment->setSubject('s-v3');
     $this->em->persist($comment);
     $this->em->flush();
     $article2 = new RelatedArticle();
     $article2->setTitle('a2-t-v1');
     $article2->setContent('a2-c-v1');
     $comment->setArticle($article2);
     $this->em->persist($article2);
     $this->em->persist($comment);
     $this->em->flush();
     $comment->setMessage('m-v5');
     $this->em->persist($comment);
     $this->em->flush();
     $this->em->clear();
 }
 public function addComment(Comment $comment)
 {
     $comment->setArticle($this);
     $this->comments[] = $comment;
 }